The Method For Analyzing Expiratory Signals And Its Application In Pulmonary Function Testing

Chronic obstructive pulmonary disease (COPD), characterized by persistent airflow limitation, can be prevented and treated by early detection and intervention. Pulmonary function testing has been considered as the gold standard of the diagnosis of COPD by Global Initiative for Chronic Obstructive Lung Disease (GOLD). However, the current missed diagnosis rate of COPD is very high, of which the main reason is that pulmonary function testing has not been universal. One hand, only2A or above grade hospital has the economic ability to buy a large and imported volume scanner with high price, while there is still a gap in the measurement accuracy and precision between domestic independent instruments and imported instruments. On the other hand, the strict testing quality control standard of spirometry requires subjects aged≥10yrs to exhale for more than6seconds and achieve a plateau on the volume-time curve, which has greatly increase the difficulty obtaining tests with high quality. The current domestic situations make it difficult to generalize the spirometry in primary care. In order to popularize the spirometry in the field of public health, the studies are about the development of low-cost spirometer and reducing the difficulty of spirometry by the method for analyzing forced expiratory flow signals. The contents of the studies are as follows:1. The constuction of the aquisition system of forced expiratory flow signals based on the method of double differential pressure sensorsWe refined the requirements for the performance of the spirometer, and determined the indicators for evaluating the lung function based on fully analyzing the characteristics of forced expiratory flow signals. Since orifice plate flowmeters have the advantages in simple structure, convenient manufafure and use, and low cost, we proposed a design scheme of an aquisition system of forced expiratory flow signals based on the method of double differential pressure sensors. The flowmeter used in the system overcame the low measuring range of the traditional orifice plate flowmeters. Its maximum measurable expiratory flow is12L/s, and minimum detectable expiratory flow can reach7mL/s. At the same time, the low cost advantage ensures the feasibility of the application and popularization of this system.2. Repetitive studies of the aquisition system of forced expiratory flow signalsThe influence of the operator on the pulmonary function testing results and the short-term repeatability of the system were evaluated by the two consecutive days of pulmonary function testing of35subjects conducted by two operators, while the medium-term repeatability was evaluated by the six-month calibriations with a3-L calibriation syringe. Results shows that pulmonary function testing results are not determinated by operators as long as the subjects can fufill the testing quality control standard of spirometry recommended by the America Thoracic Society/European Respiratory Society; the short and medium-term reproducibility study proves that the system has good short and mid-term stability.3. The study of the method for analyzing forced expiratory flow signals based on the forced expiratory mathematical model and its applicationsIn this study, the combination of the lumped parameter model of FVC maneuver and the new Luus-Jaakola (NLJ) optimization procedure was applied to the estimation of FVC by analyzing the early part of the forced expiratory flow-time (FEFT) curve. FEFT curves from90subjects with and without respiratory disease were used to validate the method. The results show that the difference between FVCest and FVCmea decreased with the length of chosen curves increasing. When the length of chosen curves reached3s, FVCest and FVCmea can fulfill the repeatability criteria recommended by American Thoracic Society/European Respiratory Society (ATS/ERS). Since early termination of exhalation is a common problem in pulmonary function testing, the performance of this method in practical application was evaluated by analyzing103unacceptable FEFT curves because of early termination of exhalation. The results show that This method can be used to analyze the unacceptable spirometry because of early termination of exhalation, and also can help the subjects who cannot complete the forced expiratory maneuver to provide a reliable estimate of FVC.4. The study on the correlation between lung function and arterial elastic functionThe association of impaired pulmonary function with the risk of cardiovascular mortality has been reported in several prospective studies. However, the nature of this association and the mechanisms underlying it are unknown. The aim of this study was to investigate the relationship between artery elastic function and lung function indicators. First, a new method based on the2nd-order B-spline wavelet for calculating augmentation index (AIx) was proposed (named convolution method) and pulse waveforms derived from60healthy subjects were used to validate this method. The results show that the convolution method described in this study can accurately calculate AIx without any low-pass filter algorithm even when the pulse signal contains high-frequency noises. Second, we analyzed the correlation between the AIx of radial pulses (rAIx) and lung age for men by the cardiovascular elasticity function tests and spirometry derived from106men. The results show that rAIx increases with lung age before70years and this increase slows down after70years and plateaus later. Lung age can better reflect the relationship between artery elastic function and lung function for men, which further stresses the importance of pulmonary function testing.